Orthogonal frequency-divisional multiplexing (OFDM) signaling schemes often are used in wired and wireless systems to facilitate high-bandwidth data transmission. Generally, OFDM is a multi-carrier modulation technique that partitions the bandwidth of an OFDM channel into a plurality of orthogonal subchannels, which are also commonly referred to as tones, bins, and subbands. Each subchannel is associated with a subcarrier that may be modulated with data such that N modulation symbols may be transmitted on the N subchannels for each OFDM symbol period. OFDM may be used in systems whereby multiple transmit nodes concurrently transmit to a receive node. Such schemes are referred to as multiple-access OFDM, or OFDMA. In OFDMA systems, each transmit node is assigned a corresponding number of the subchannels of each OFDM symbol period, during which the transmit node can modulate a corresponding OFDM symbol onto each of its allocated subchannels.
To facilitate accurate decoding of the symbols at the receive node, OFDM makes use of pilot tones, which are used by the receive node to estimate phase noise, frequency offset, and other channel conditions, and from these estimated channel conditions tune the symbol decoding process. However, while the use of pilot tones facilitates accurate characterization of the channel conditions, each pilot tone displaces actual data in an OFDM symbol, and thus a balance between robust decoding and data throughput typically is sought in selecting the number of pilot tones to be used in an OFDM symbol. In many conventional OFDM-based systems, such as IEEE 802.11 (WiFi) and IEEE 802.16 (WiMAX) wireless systems and Multimedia over Coaxial Alliance (MoCA) systems, the subchannels to be used for pilots typically are evenly distributed across the OFDM symbol in an attempt to broadly characterize the entire channel in view of the frequency-dependent fading often present in such systems, and in a manner independent of the allocation or use of the subchannels among the various transmit nodes.